Search

Using high dose implantation of 200 keV Co ions followed by high temperature annealing, we have created buried layers of CoSi2 in crystalline Si of both (100) and (111) orientations. For a dose of 3 × 1017 Co/cm2, the layer that forms is ∼1100Å thick and the overlying Si is ∼600Å thick. A lower dose of 2 × 1017 Co/cm2 yields a thinner layer, 700Å thick, under 1200Å of crystalline Si. Rutherford Backscattering and channeling analysis of the layers shows that they are aligned with the substrate (χmin of the Co as low as 6.4%.) and TEM inspection of the (100) CoSi2/Si interfaces shows that they are abrupt and epitaxial (with occasional small facets). Moreover, electrical characterization of these layers yields resistance ratios that are better than epitaxial CoSi2 films grown by more conventional UHV methods.

Recent progress in the growth of thin epitaxial silicides on silicon has resulted in films of very high quality with especially smooth interfaces. Using a completely different technique, high dose implantation followed by annealing, we have succeeded in creating buried single-crystal layers of CoSi2, NiSi2, and CrSi2 in crystalline silicon. The CoSi2 and NiSi2 layers grow in both the (100) and (111) orientations--those in (111) have better crystallinity, but those in (100) are of higher electrical quality. The CrSi2, on the other hand, only grows in the (111) orientation where its hexagonal structure has an almost perfect lattice match to silicon. We call this new internal growth process “mesotaxy” by analogy with epitaxy which refers to single-crystal growth on surfaces.

We have fabricated tunnel junctions between chemically etched single crystals of YBa2Cu3O7-δ and evaporated metal counterelectrodes which exhibit reproducible characteristics. Above the bulk critical temperature of YBa2Cu3O7-δ, Tc, the conductance, G(V), has a linear dependence with voltage and has some asymmetry. Below Tc, additional structure associated with the superconductivity appears in G(V). At T>>Tc there is a reproducible finite zero bias conductance.

We have prepared low leakage tunnel junctions on epitaxial YBa2Cu3O7 (YBCO) films grown on SrTiO3(001) by evaporating Pb counterelectrodes onto chemically etched YBCO surfaces. Structure in the voltage dependence of the tunneling conductance is reproducible and strongly resembles what has been obtained in similarly etched junctions on YBCO single crystals.